Limitations of feeding fats to early lactation cows
As a general rule of thumb, unsaturated fatty acids such as those found in canola oil are relatively toxic to the rumen microbes. This is especially true for forage-fibre digesting species. With that being said, this doesn't mean that canola oil or other types of unsaturated fatty acids should not be fed to dairy cows. Most rumen microbes have the ability to detoxify and reduce the toxic effect of unsaturated fats through a process called "bio-hydrogenation". However, large amount of unsaturated fatty acids (approximately 450g/head/d) can overwhelm this process, causing negative effects on the rumen microbial population.
In order to compliment added saturated or unsaturated fats from natural feedstuffs during early lactation stage of the dairy cows, commercial "rumen bypass fats" can be added. They are chemically inert, and hence are able to pass through the rumen without affecting fermentation, but can still be digested in the cow's intestine. In general, they are 3 types of bypass fats. The first being 99% bypass fats. They have the highest energy density, made up of 99% fats which are able to pass through the rumen without changing their solid state. Next, is calcium soap, also known as calcium salts of fatty acids. As the name suggests, it is made by reacting fatty acids with calcium. It bypasses the rumen, but is broken down in the abomasum to release the fat and calcium for digestion. Then there are other types of fats which usually have around 50% fats. They are cheaper but they are poorer in value compared to 99% bypass fats of calcium soap.
Regardless of the kind of commercial fat supplement chosen to add into the cow's diet, it is crucial to avoid overfeeding fats to early lactation cows. It is important for the farmers to ensure that the diet is still well balanced with carbohydrates, protein, water and mineral to support the health and normal activities of the resident microbes in the rumen.
Problems to lookout for
Here are some potential problems to lookout for when feeding excessive amounts of fats to lactating cows:
1) Inconsistent dry matter intake - Research shows that by overfeeding fats to lactating cows, this could potential satisfy the cow's natural appetite for feed. Hence, this may reduce the rate of feed digestion and passage (bypass fats) in the lower guts.
2) Milk fat depression (MFD) - As mentioned above, by feeding excessive unsaturated fats to dairy cows, this could cause reduction in acetate/butyrate production that contributes to the milk fat production. Some research also shows that too much tallow or vegetable oil can coat forage fibre practices in the rumen and allow incomplete fermentation.
3) High milk urea nitrogen (MUN) - By over-feeding bypass fats to the lower gut while simultaneously starving the rumen microbes of available starch could lead up to potential problems such as incomplete protein digestion and large amounts of urea to be released to the rumen. High MUN levels are linked to lower conception rates in dairy cattle.
All in all, if the diets for lactating cows are well balance, the problems mentioned can be avoided. Adding fats to the diet provide tremendous value in terms of increased in milk and milk fat yield but it should complement the rest of the dairy diet. Such success should help increase the profitability of the farmers.